1. Field of the Invention
The present invention relates to an LCD device, and more particularly, to an LCD device which is driven with a small number of data lines in comparison with the background art. The present invention also relates to a 2-dot inversion method of driving an LCD device, thereby preventing deterioration in image quality caused by a specific pattern.
2. Description of the Background Art
Display devices as visual information transfer media have gained more importance in an information oriented society. Among them, liquid crystal display (LCD) devices have rapidly replaced traditional cathode ray tubes (CRT) devices as the next-generation of display devices because superior legibility, low power consumption and high definition.
An LCD device includes an LCD panel for displaying an image, a driving unit for driving the LCD panel, and a back-light unit for supplying light to the LCD panel.
Liquid crystals used in the LCD device are not light emitting materials, which emit light by themselves, but rather are light receiving materials, which pass light from the outside by various transmittance to allow an image to be displayed on a screen. Accordingly, a back-light unit, e.g. a separate light source, is provided in the LCD device.
FIG.1 illustrates an LCD device in accordance with the background art. As shown in FIG. 1, the LCD device includes: a plurality of data lines (DL1˜DL4) vertically disposed on a substrate; a plurality of gate lines (GL1˜GL4) horizontally disposed on the substrate; and a plurality of pixels (R, G and B) divided according to the data lines (DL1˜DL4) and the gate lines (GL1˜GL4), perpendicularly crossing each other.
The pixels (R, G and B) are disposed in a matrix format on the substrate, in which a red pixel (R), a green pixel (G) and a blue pixel (B) are repetitively disposed. Switching devices (SW1) such as thin film transistors (TFTs) are individually provided at the pixels (R, G and B). The pixels in a column are connected with a corresponding data line (DL1˜DL4) by respective switching devices (SW1). The pixels in a row are connected with a corresponding gate line (GL1˜GL4) by respective switching devices (SW1). More specifically, gate electrodes of the switching devices (SW1) connect with the gate lines (GL1˜GL4), and source electrodes of the switching devices (SW1) connect with the data lines (DL1˜DL4), and drain electrodes of the switching devices (SW1) connect with pixel electrodes 10.
Common electrode lines (CL1˜CL3), in parallel with the gate lines (GL1˜GL4), are individually disposed on the substrate. The common electrode lines (CL1˜CL3) partially overlap the pixel electrodes 10, provided at the respective pixels (R, G and B). Common electrodes are provided at parts of the common electrode lines (CL1˜CL3) overlapping the pixel electrodes 10, and a common voltage is supplied through the common electrode lines (CL1˜CL3). An electric field caused by a voltage differential is formed between the pixel electrode 10 and the common electrode.
As scan signals are sequentially supplied to the gate lines (GL1˜GL4) from a gate driving unit in the LCD device, the switching devices (SW1) connected to the corresponding supplied gate line (GL1˜GL4) are all turned on. In addition, image data, outputted from a data driving unit and transmitted through the corresponding data lines (DL1˜DL4) during a period when the switching devices (SW1) are turned on, is supplied to the pixels (R, G and B) through the switching devices (SW1). The image data supplied to the pixels (R, G and B) is applied to the pixel electrodes 10.
Each common electrode corresponding to each pixel (R, G and B) receives a common voltage through the common voltage lines (CL1˜CL3). When the voltage is supplied to the pixel electrode (10) and the common electrode as described, an electrode field caused by a voltage differential is formed between the pixel electrode and the common electrode to thereby rearrange liquid crystals of the corresponding pixels (R, G and B) and control light transmittance, whereby an image having desired luminance is implemented at the pixels (R, G and B).
When a certain electric field is continuously applied to a liquid crystal layer of the LCD device, liquid crystals are deteriorated and undesirable after-images are generated by a DC voltage component. Accordingly, in order to prevent deterioration in the liquid crystals and get rid of the DC voltage component, positive and negative voltages of image data are repeated and supplied on the basis of the common voltages. Such a driving method is referred to as an inversion method.
The inversion driving method can be classified into several types. In a frame inversion method, the polarity of image data is inverted by a unit of one frame of an image and supplied. In a line inversion method, the polarity of image data is inverted by units corresponding to gate lines and supplied. In a dot inversion method, the polarity of image data according to pixels adjacent to each other is inverted and supplied, and further the polarity of image data is inverted by a unit of one frame of an image and supplied. Among the several types of inversion driving methods, the dot inversion method performs well at preventing deterioration in image quality, and is the most widely used.
In the LCD device illustrated in FIG. 1, an image is implemented on a screen by the dot inversion method by supplying image data having different polarities through every odd numbered data line (DL1, DL3, . . . ) and every even numbered data line (DL2, DL4, . . . ) of the data lines (DL1˜DL4). When the image data, having polarities opposite to each other, is supplied to adjacent pixels according to the smallest unit comprising a red pixel (R), a green pixel (G) or a blue pixel (B), the method is referred to as a 1-dot inversion method. Compared to the line inversion method or the frame inversion method, the 1-dot inversion method produces less deterioration in image quality. However, the 1-dot inversion method still experiences some deterioration in image quality, such as deterioration due to crosstalk. In particular, serious deterioration in image quality can be caused in an image where a specific pattern repetitively appears, as shown in FIG. 2A or FIG. 2B.
FIG. 2A is a diagram illustrating one example of polarities of pixels arranged on a screen and FIG. 2B is a diagram illustrating another example of polarities of pixels arranged on the screen, in accordance with the background art. The 1-dot inversion method is used in the screens of FIGS. 2A and 2B, in which specific patterns in black and white are shown. FIG. 2A illustrates a screen in which a vertical pattern appears, and FIG. 2B illustrates a screen in which a checkerboard pattern appears. When the vertical pattern is implemented on the screen as shown in FIG. 2A, a specific pattern occurs regularly, whereby image data having one polarity is supplied to the pixels (P10) of a line unit.
A specific pattern is also shown in the checkerboard pattern of FIG. 2B. Image data having one polarity is applied to the pixels (P10) of a line unit. However, in FIG. 2A, the pixels (10) of the line unit alternately receive positive image data and negative image data, and in FIG. 2B, one of positive image data and negative image data is supplied to the entire pixels (P10).
As described above, one polarity is strongly applied to the pixels (P10) of a line unit, which may cause a voltage change in the common voltage lines corresponding to the pixels (P10) of the line unit. For example, when more positive image data is supplied to the pixels of the line unit than negative image data, a voltage level of the common voltage lines may increase in comparison to its original voltage level. When more negative image data is supplied thereto, a voltage level of the common voltage lines may decrease in comparison to its original voltage level. Such a voltage change changes the size of the electric field applied to the liquid crystals, causing horizontal crosstalk in which a horizontal stripe occurs on the screen.
As described above, in the LCD device, the pixels (R, G and B) of a line unit individually correspond to the gates lines (GL1˜GL4), and the pixels (R, G and B) of a column unit individually correspond to the data lines (DL1˜DL4), to receive scan signals and image data, respectively. In order to obtain high resolution in an LCD device, fabricated to have a large area and high resolution, the number of gate lines (GL1˜GL4) and the number of data lines (DL1˜DL4) should be increased. This increases fabrication costs.